linux-kernel - Re: [PATCH 4/4] arm64: gicv3: its: Increase FORCE_MAX

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Date:	Tue, 12 May 2015 18:20:49 +0200
From:	Robert Richter <robert.richter@...iumnetworks.com>
To:	Will Deacon <will.deacon@....com>
CC:	Robert Richter <rric@...nel.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Tirumalesh Chalamarla <tchalamarla@...ium.com>,
	Radha Mohan Chintakuntla <rchintakuntla@...ium.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/4] arm64: gicv3: its: Increase FORCE_MAX_ZONEORDER for
 Cavium ThunderX

Will,

On 12.05.15 13:30:57, Will Deacon wrote:
> On Mon, May 11, 2015 at 10:14:38AM +0100, Robert Richter wrote:
> > On 05.05.15 11:53:29, Will Deacon wrote:
> > > On Sun, May 03, 2015 at 09:49:32PM +0100, Robert Richter wrote:
> > > > From: Radha Mohan Chintakuntla <rchintakuntla@...ium.com>
> > > > 
> > > > In case of ARCH_THUNDER, there is a need to allocate the GICv3 ITS table
> > > > which is bigger than the allowed max order. So we are forcing it only in
> > > > case of 4KB page size.
> > > 
> > > Does this problem disappear if the ITS driver uses dma_alloc_coherent
> > > instead? That would also allow us to remove the __flush_dcache_area abuse
> > > from the driver.
> > 
> > __get_free_pages() is also used internally in dma_alloc_coherent().
> > 
> > There is another case if the device brings dma mem with it. I am not
> > sure if it would be possible to assign some phys memory via devicetree
> > to the interrupt controller and then assign that range for its table
> > allocation.
> > 
> > Another option would be to allocate a hugepage. This would require
> > setting up hugepages during boottime. I need to figure out whether
> > that could work.

For allocation of 16MB cont. phys mem of a defconfig kernel (4KB
default pagesize) I see this different approaches:

 * set FORCE_MAX_ZONEORDER to 13 as default,

 * set FORCE_MAX_ZONEORDER to 13 if ARM_GIC_V3 is set,

 * set FORCE_MAX_ZONEORDER to 13 if ARCH_THUNDER is set (this patch),

 * use hugepages if enabled (defconfig has the following options
   enable: CGROUP_HUGETLB, TRANSPARENT_HUGEPAGE, HUGETLBFS, this might
   work with current default kernel without changing defconfig
   options),

 * use devicetree to reserve mem for gicv3 (need to check ACPI).

Do you see any direction?

> > What about on the remaining 3 patches?
> 
> Marc would be the best guy to review those, but he's on holiday for a couple
> of weeks at the moment.

Thanks for the note and your comments.

-Robert
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